The proventriculus of Cicindelidae : systematics and functional morphology

Abstract

Internal structures of the proventriculus of adult tiger beetles were examined to determine their function and taxonomic and phylogenetic value. The overall appearance of the proventriculus suggested an intricate filter designed to permit the flow of nutrient fluids into the midgut while retaining particulate food; this corroborates earlier hypotheses of tiger beetle feeding behaviour. The intricate proventricular structure indicates that regurgitation of midgut liquids does not occur during regular feeding. S.E.M. and light microscope observations revealed eight longitudinal internal folds, four minor and four major plicae, lined with ctenidia. The minor plicae become apodemes posteriorly and displayed anteriorly directed ctenidia which were shown to vary among cicindelid subgenera. The ctenidia of the major plicae varied in length independently of the plical height at both the anterior and posterior regions of the organ. Slopes which were calculated from these measurements describe the inner proventricular structure between the anterior and posterior ends of the proventriculus and were shown to differ among cicindelid subgenera and species groups. Advanced taxa displayed flatter proventricular slopes. The proventricular slope data were compared to habitat types of seventeen species. Among classified species of the maritima group, proventricular slopes reflected traditional phylogenetic relationships rather than habitat distinctiveness. Significant differences of proventricular slopes were shown among species groups having different ancestral habitats. A histological examination of the foregut of Cicindela tranquebarica Herbst third instar larva revealed that the proventriculus is absent at this stage. The overall structure of the proventriculus of the primitive tiger beetle Omus audouini Reiche displayed the close phylogenetic relationship of this genus with the genus Cicindela although some variations were noted. By comparison, in adults of the carabid Carabus nemoralis Muller, "socketed setae" and cuticular ctenidia covered the intima of this organ. Based on the comparative morphology of the proventriculus, members of Omus and Cicindela were concluded to demonstrate a phylogenetic relationship, with Carabus nemoralis more distantly related.